In the event of a car accident, you want your headrest in the proper position to prevent injury to your neck, such as whiplash. Simply put, whiplash occurs when the force of a crash causes your head and neck to violently snap back and forth. A headrest can prevent your head and neck from snapping back.
If your headrest is ajustable, adjust it so that the top middle of the rest is level with the height of your eyes. It takes a few seconds and can prevent significant injuries to your neck in the event of a car crash.